Isoelectronic metal fluoride transition state analogue (TSA) complexes, MgF3 - and AlF4 -, have proven to be immensely useful in understanding mechanisms of biological motors utilizing phosphoryl transfer. Here we report a previously unobserved octahedral TSA complex, MgF3(H2O)-, in a 1.5 Å resolution Zika virus NS3 helicase crystal structure. 19F NMR provided independent validation and also the direct observation of conformational tightening resulting from ssRNA binding in solution. The TSA stabilizes the two conformations of motif V of the helicase that link ATP hydrolysis with mechanical work. DFT analysis further validated the MgF3(H2O)- species, indicating the significance of this TSA for studies of biological motors.
© 2021 The Authors. Published by American Chemical Society.